1. Field of the Invention
The subject invention generally pertains to electronic power conversion circuits, and more specifically to high frequency, switched mode power electronic converter circuits.
2. Description of Related Art
One significant source of power losses in high frequency power converters is gate drive loss. Some converters have the inherent ability to provide synchronous rectifier self gate drive which results in the recirculation of gate drive energy and easy synchronous rectifier gate drive. Without a self gate drive mechanism driver circuits are required and, in many cases, these driver circuits can be complex and costly. What is needed is a simple synchronous rectifier self gate drive mechanism for zero voltage switching (ZVS) converter topologies.
In most cases a positive voltage is applied to the gate during the on state of the switch. The positive voltage should be sufficient to fully enhance the switch, but no more. Often a negative gate voltage is applied to the gate during the off state of the switch. The negative gate drive speeds up the turn off transition by increasing the current out of the gate during the transition. There is no advantage to having a negative gate voltage. The switch is fully off at zero volts or at any voltage below the gate source threshold voltage. What is needed is a circuit that can provide the high current benefits of negative gate drive, but terminate the drive current soon after the gate voltage has dropped below the threshold voltage, thereby saving gate charge and energy and providing gate negative over voltage protection.
An object of the subject invention is to provide a simple self gate drive mechanism for synchronous rectifiers which recirculates rather than dissipates gate drive energy for synchronous rectifiers.
Another object of the subject invention is to provide a simple circuit mechanism that limits the amount of gate drive energy and protects the synchronous rectifier from negative gate voltage breakdown.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
These and other objects of the invention are provided by novel circuit techniques that use the small inductor employed in many ZVS circuits to provide a synchronous rectifier self gate drive mechanism. Synchronous rectifier self drive is provided by coupling a capacitor to the same small inductor used to provide drive energy for ZVS. Alternatively, the self gate drive signal can be provided by a magnetically coupled winding of the same small inductor used to provide drive energy for ZVS.